Ferromagnetic compounds and method of preparation



United States Patent ABSTRACT OF THE DISCLOSURE The new rare earthcompounds: Gd Bi, Gd Sb and Dy Sb and their solid solutions: Gd (Bi Sband (Gd Dy (Sb Bi are prepared. The constituent elements are powdered,mixed and heated in an airtight crucible to a temperature of 1300 C. andthen cooled to room temperature. The new compounds and their solidsolutions are ferromagnetic and exhibit varying Curie temperatures. Themembers of the class can be used in thermal control and safety devices.

This invention relates to new rare earth compounds and, moreparticularly, to those compounds having the formula: Gd Bi, Gd Sb and DySb and solid solutions thereof. These new compounds either When pure orin solid solutions are ferromagnetic.

The rare earth metals and their compounds are important magneticmaterials because they exhibit higher magnetic moments than the irongroup metals (e.g., Fe, Co, and Ni) and their compounds.

The magnetic moment of the rare earth elements is either the sum ordifference of the spin and orbital moments of theunpaired electrons inthe 4f shell, the difference resulting for the lighter and the sum forthe heavier elements. The outer bonding orbitals effectively shield the4f shell so that chemical bond formation has little effect on the totalmagnetic moment. In contrast, the unpaired 3d electrons of the irongroup metals are directly involved in bond formation and magnetic cupling so that'compounds and alloys of these elements generally havedifferent moments.

Heretofore, most investigations of rare earth systems with Group V,elements (e.g., N, P, As, Sb, and Bi) have been confined to the study of1:1 compounds (Iandelli, A., Rare Earth Research, Macmillan, New York,1961, pages 135-151) or rare earth rich systems of the lighter rareearths (La and Ce) (Gschneidner, Rare Earth Alloys, Van Nostrand, NewYork, 1961, pages 11l1l5).

An example of rare earth rich systems can be found in application S.N.299,180 entitled Ferromagnetic Compounds and Method of Preparation, byF. Holtzberg, et al.

It is an object of the invention to prepare ferromagnetic compounds.

It is another object of the invention to prepare new rare earthcompounds which are ferromagnetic.

It is a further object of the invention to prepare rare earth compoundshaving the formula Gd Bi, Gd Sb and Dygsb.

Still another object of the invention is to prepare rare earth solidsolution systems which are ferromagnetic.

Another object of the invention is to prepare a ferromagnetic compoundhaving the formula Gd Bi.

Still another object of the invention is to prepare a ferromagneticcompound having the formula Gd Sb.

Patented Sept. 19, 1967 Still another object of the invention is toprepare a ferromagnetic compound having the formula Dy Sb.

The foregoing and other objects, features and advantages of theinvention will become apparent from the more particular description of apreferred embodiment of the lnvention.

The rare earth compounds of the invention have the formula Gd Bi, Gd Sband Dy Sb and crystallize with a hexagonal structure.

Pure rare earth metal ingots (99.9 percent pure) of Gd and Dy are filedinto powders in a dry oxygen free atmosphere (e.g., He, Ar, N). Rareearth metal filings are then mixed with antimony or bismuth metal (99.9percent pure) and pressed into pellets which are then placed in acrucible which is made of a material which does n t enter into thereaction (e.g., tantalum or molybdenum). The size of the pellet is suchthat the pellet provides a piston fit to the crucible. A tapered plug ofcrucible material is forced into the crucible so that it presses 0n thesurface of the pellets in order to exclude as much dead (i.e., empty)volume as possible. The tight fit and small particle size are necessarybecause if there is dead (or empty) space in the crucible the Sb or Bivapor will condense out on cooling and result in inhomogenous 'products.If the particles are too large, the high reaction temperature willvaporize the Sb or Bi before the reaction is completed and force thevapor out of the crucible. The excess tantalum above the plug is thenpeened over to form a tight closure so that Bi or Sb vapor pressureproduced during the reaction can be contained within the crucible. Thecrucible is then placed on a pedestal in a quartz vacuum system centeredin a radio frequency induction heating coil. An ambient atmosphere ofhelium is often used in place of the vacuum. Power is delivered to thecoil at a rate such that the crucible temperature rises to 1300" C.within approximately 10-30 seconds. The temperature is maintained at1300 C. for 15 minutes and the sample is then cooled to roomtemperature. When the tantalum crucible is opened, the compound appearsas a dense metallic ingot.

The new rare earth compounds are brittle metallic materials whichoxidize slowly when exposed to air and are pyrophoric in finely powderedform.

Although the chemistry of the rare earths is relatively uniform, thereare differences in the crystallization which can arise from thedifferences in radii and probably from differences in electronicconfigurations. Certain compounds herein described result as the primarycrystallization from the melt and required no further heat treat-.

Example IGd Bi 3.1454 grams of Gd is filed into a fine powder in a drybox and the filings mixed with 2.0900 grams of powdered bismuth metal.The mixture is then pressed into pellets in a nitrogen purged dry box.These pellets are then placed in an out-gassed tantalum crucible. Thetapered tantalum plug is forced into the crucible so that it presses onthe surface of the pellet in order to exclude as much dead volume aspossible. The excess tantalum above the plug is then peened over to forma gas-tight closure. This crucible is now placed on a pedestal in aExample II-Gd Sb The procedure of Example I is repeated except that1.217 5 grams of antimony are substituted for the bismuth. The resultantproduct is Gd Sb.

Example lIl-Dy Sb 3.2500 grams of Dy is filed into a fine powder in adry box and the filings mixed with 1.2175 grams of powdered antimony.This mixture is then pressed into pellets in a nitrogen purged dry box.These pellets are then placed in an out-gassed tantalum crucible. Thetapered tantalum plug is forced into the crucible so that it presses onthe surface of the pellet in order to exclude as much dead volume aspossible. The excess tantalum above the plug is then peened to form agas-tight closure. This crucible is now placed on a pedestal in a quartzvacuum system centered in a RF. induction coil. The temperature of thecrucible is raised to 1400 C. and held there for 15 minutes. Then thecrucible is rapidly cooled to room temperature. The resultant product isDy Sb.

Dy Sb has a positive paramagnetic Curie Temperature (0 of 110 K. whichindicates at least a partial ferromagnetic interaction.

Solid solution systems of the rare earth compounds of the invention havethe formulas:

These rare earth solid solution systems are ferromagnetic and sincetheir Curie temperatures are a rapidly varying function of compositionthey can be used to prepare a series of materials with Curietemperatures rarbitrarily selected from a continuous range of Curietemperatures and thus find application in thermal control and safetydevices. The solid solution systems are prepared in much the same manneras the rare earth compounds.

The initial mixture is prepared by weighting and thoroughly mixing thecomponent materials (i.e., rare earths and metalloids) in finely dividedform as specified for any of the examples set forth in Table I. Themixture is then pressed into pellets and heated in a sealed tantalumcrucible as in the procedure set forth for the pure compounds asprepared in Example I.

The solid solution systems prepared as shown in Examples 1VVI have theformula for each of the respective examples.

The procedure of Example I is followed except that the quantitiesindicated for each example in Table I are used, intimately mixed andthen pressed into pellets. The resulting products is a solid solutionsystem having the formula indicated for each example.

TABLE I The solid solutions show a linear variation of lattice constantwith z Which can be used to determine the ratio of Gd to Dy. The Curietemperature varies as a function of concentration of the rare earthatom. The magnetic moments of the solid solutions are an average of theindividual rare earth moments Weighted on the basis of theirconcentrations.

The solid solutions Gd (Bi Sb (Gd Dy Sb, and (Gd Dy Sb Bi have theaverage physical properties of the above solid solutions, i.e., theaverage moment of the rare earth part of the solid solution will varyrapidly as a function of the Sb and Bi concentration or conversely givena ratio of Sb to Bi the moment is the average of the moments of Gd andDy according to their concentr-ations.

The invention herein described results in new rare earth compoundshaving the formulas, Gd Bi, Gd Sb, Dy Sb, z( 1 X X), 1z yz) 2 and 1 zyz) 2 1-x x and their preparation. As has been shown, these compoundseither in their pure state or in solid solution systems areferromagnetic.

While the invention has been particularly described with reference topreferred embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention.

What is claimed is:

1. A rare earth compound selected from the group consisting of Gd Bi, GdSb and Dy Sb.

2. The rare earth compound Gd Bi.

3. The rare earth compound Gd Sb.

4. The rare earth compound Dy Sb.

5. The process of preparing a rare earth compound selected from thegroup consisting of Gd Bi, Gd Sb and Dy Sb which comprises:

(a) mixing together in finely divided form the rare earth constituentand the Group VA constituent of said rare earth compound in a 2:1 molarratio;

(b) heating the thus formed mixture in a sealed crucible in a vacuum toa temperature of 1300 C. thus initiating a reaction;

(c) cooling to room temperature upon completion of said reaction.

6. A rare earth solid solution system having a for- 7. A rare earthsolid solution system having a formula Gd (Sb Bi where 1 x 0.

8. A rare earth solid solution system having a formula (Gd Dy (Sb Biwhere 1 z 0 and l x 0.

9. The rare earth solid solution system having the formulaGd Bi Sb 10.The rare earth solid solution system having the formula (Gd Dy Sb.

11. The rare earth solid solution system having the formula orz ua)2(o.5 0.5)-

12. The process of preparing a rare earth solid solution system havingthe formula (Gd Dy Sb where 1 z 0 which comprises:

(1) mixing together in finely divided form Gd, Dy and Sb in proportionssuch that the solid solution system produced by heating has the aboveformula;

(2) heating the thus formed mixture in a sealed tantalum crucible placedin an evacuated quartz radio frequency induction heater to a temperatureof 1300 C. thus initiating a reaction;

(3) cooling to room temperature on completion of said reaction.

13. The process of preparing a rare earth solid solution system havingthe formula Gd Sb Bi where l x 0 which comprises:

(1) mixing together in finely divided form Gd, Sb

and Bi in proportions such that the solid solution system produced bytreating has the above formula;

(2) heating the thus formed mixture in a sealed tantalum crucible placedin an evacuated quartz radio frequency induction heater to a temperatureof 13 00 C. thus initiating a reaction;

(3) cooling to room temperature on completion of said reaction.

14. The process of preparing a rare earth solid solution system havingthe formula (Gd Dy (Sb Bi Where 1 z 0 and 1 x 0 which comprises:

(1) mixing together in finely divided form Gd, Dy, Sb and Bi inproportions such that the solid solution system produced by treating hasthe above formula;

(2) heating the thus formed mixture in a sealed tantalum crucible placedin an evacuated quartz radio frequency induction heater to a temperatureof 1300 C. thus initiating a reaction;

(3) cooling to room temperature on completion of said reaction.

References Cited UNITED STATES PATENTS DAVID L. RECK, Primary Examiner.RICHARD O. DEAN, Examiner.

1. A RARE EARTH COMPOUND SELECTED FROM THE GROUP CONSISTING OF GD2BI,GD2SB AND DY2SB.